Lean burn gas engines recently attract attentions in the maritime industry because they can reduce emissions such as NOx, SOx and CO~2~. On the other hand, since methane (CH~4~) is the main component of natural gas, the slipped methane which is the unburned methane emitted from the lean burn gas engines might have a potential impact on global warming. It is therefore important to make a progress on the exhaust aftertreatment technologies for lean burn gas engines. As a countermeasure for the slipped methane, Palladium (Pd) catalyst for CH~4~ oxidation can be expected to provide one of the most feasible methods because Palladium (Pd) catalyst for CH~4~ oxidation can activate in the lower exhaust gas temperature. However, recent studies have shown that the reversible adsorption by water vapor (H~2~O) inhibits CH~4~ oxidation on the catalyst and deactivates its CH~4~ oxidation capacity. In order to apply the Pd catalyst for reducing the slipped methane in exhaust gas of lean burn gas engines, the deactivation in the higher H~2~O concentration should be overcome.

It can be known that the CH~4~ oxidation performance is influenced by active sites on the Pd catalyst. However, measuring methods for active sites on Pd catalyst under exhaust gas conditions could not be found. Authors thus proposed a dynamic estimation method for the quantity of effective active sites on Pd catalyst in exhaust gas temperature using water-gas shift reaction between the saturated chemisorbed CO and the pulse induced H~2~O. Because both of CH~4~ and CO oxidation processes on Pd catalyst share with the same active sites based on Mars-van Krevelen mechanism, the saturated chemisorbed CO molecular can provide the quantity of effective active sites on Pd catalyst in exhaust gas temperature using with a stoichiometry of Pd/CO=1.

The previous study clarified the relationship between adsorbed CO volume and Pd loading in gas engine exhaust gas temperature and revealed the effects of flow conditions on the estimation of adsorbed CO volume. However, effects of support materials on the estimation of adsorbed CO volume were not revealed. In order to improve CH~4~ oxidation performance on Pd catalyst under exhaust gas conditions, it is important that effects of support materials on active sites should clarify.

This paper introduced experimental results of estimation of absorbed CO volume on different support materials of Pd catalysts by using the dynamic evaluation method. Experimental results show that chemisorbed CO volume on Pd/Al~2~O~3~ catalyst exhibits higher chemisorbed CO volume than that of Pd/SiO~2~ and Pd/Al~2~O~3~-SiO~2~ catalyst in 250-450 ºC. These results can provide a part of the criteria for the application of Pd catalyst for reducing the slipped methane in exhaust gas of lean burn gas engines.


Effect of Support Materials on Pd Methane Oxidation Catalyst Using Dynamic Estimation Method

Division / Sponsors: 
Internal Combustion Engine Division (ICED)

Paper Proceedings: https://asmedigitalcollection.asme.org/ICEF/ICEF2020/volume/84034

ICEF2020 - Virtual Conference

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.